The present invention relates to improvements in joint prostheses; more particularly to improvements in shoulder joint prostheses which employs a collarless design.
Shoulder joint prostheses are known in the art. See, for example, U.S. Pat. Nos. 4,919,669 and 5,738,161, hereby incorporated by reference. A typical shoulder prosthesis comprises a body, which is for implantation into a prepared humerus, and a head, which is fixed to the body and provides a bearing surface. Modular shoulder prostheses are also known. See, for example, U.S. Pat. No. 5,314,479, hereby incorporated by reference. U.S. Pat. No. 5,314,479 discloses a modular prosthesis comprising a body, which is implanted into the humerus, and a head, which seats onto the body. The head and body can be selected independently of each other, and head/body combinations can be selected by a surgeon to provide a custom fit without carrying a large expensive inventory of prostheses. A typical modular shoulder prosthesis, such as that disclosed in U.S. Pat. No. 5,314,479, also has a collar located between the head and the body. The collar sits on the prepared proximal surface of the humerus and provides a suitable surface for supporting the head. The collar, however, occupies joint space, and as compared to an analogous prosthesis of a non-modular design, a modular prosthesis with a collar may require additional joint space. This additional joint space may cause xe2x80x9coverstuffingxe2x80x9d of the glenohumeral joint, resulting in a decrease in range of motion. Also known are modular designs which have a collar integral with the body and provide a xe2x80x9clow profilexe2x80x9d modular connection. See, for example, U.S. Pat. No. 5,489,309, hereby incorporated by reference. However, use of these prostheses still may result in overstuffing and a loss of useful articular surface.
The shoulder prosthesis of the present invention comprises a modular humeral prosthesis component employing a collarless design. A body portion of the prosthesis is provided without a collar, and it may be implanted into a prepared proximal end of a humerus such that the body sits recessed below the level of the cut proximal surface of the humerus. A head portion is provided in which a support surface of the head functions as collar by direct apposition of it to the cut proximal humerus. The modular connection is thus recessed below the proximal bone surface. By providing a modular connection which is recessed below the bone surface, the benefits of modularity may be retained, while joint overstuffing may be reduced or eliminated, and a substantially full range of motion may be achieved.
In an illustrated embodiment, the head and body are connected by a stem and socket arrangement known as a reverse morse taper design. In this illustrated embodiment, a tapered stem is provided on the head and positioned such that it extends away from the support surface. A mating socket is provided in the proximal surface of the body. Upon implantation, the tapered stem of the head seats and locks in the mating socket of the body. Because the proximal surface of the body is recessed from the proximal surface of the humerus, the space required by this modular connection is also recessed below the proximal surface of the humerus, and the modular connection does not occupy any joint space. Essentially the entire surface area of the prosthesis which is located above the cut proximal humeral bone surface may be useful articular surface area.
An alternative embodiment includes a standard taper design, in which a tapered stem extends from the body and mates with a socket located in the head. As with the reverse morse taper design, the modular connection is recessed below the proximal surface of the humerus and does not require joint space. Other coupling designs may be used and are within the scope and spirit of this invention.
Preferably, the prosthetic device of this invention is made of titanium or cobalt chrome. Alternatively, the prosthetic device of this invention can be made of other biocompatible materials which are of sufficient strength.
Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.